Triphenylmethane dyes, such as pararosaniline, may be prepared by oxidation of the condensation products of excess aniline with formaldehyde. Pararosaniline, also known as fuchsin, parafuchsin, Basic Red 9, Magenta 0, and C.I. 42500, is commercially produced via this synthesis with formation of by-products or oxidation products that have, up to this time, had no commercial value. The by-products of the triphenylmethane dye synthesis have found only limited application as colorants in situations where the by-product could be melted and blended with the substance to be colored. The by-products were also employed as colorants by dispersing them in a mixture with a solid resin or like material, as in, for example, U.S. Pat. No. 3,884,869, incorporated herein by reference. Thus, the by-product mixture could only be used as a pigment and modification of the by-products for use as a dye was unknown.
The present invention provides a process of preparing a dye composition which employs oxidation products (typically referred to as by-products) of a triphenylmethane dye synthesis and a resultant dye composition. The process includes preparing a mixture of a triphenylmethane dye and the oxidation products by reacting methylenedianiline with aniline, an oxidation catalyst, and an oxidant. Oxidation by-product as used herein is to be understood to mean the desired oxidation products of the condensation reaction, and subsequent oxidation, of methylenedianiline that are employed as the dye composition of the present invention.
The process further includes separating the oxidation products from the triphenylmethane dye to produce a solution of oxidation products; treating the solution of oxidation products with a basic compound, which is typically dissolved in water; separating unreacted aniline from the solution of oxidation products to form a mixture of oxidation products; and sulfonating the mixture of oxidation products to form a dye composition.
The present invention also provides a process of dyeing protein-based fibers and the resultant colored protein-based fibers. The process includes providing a dye composition prepared according to the process steps as set forth above; immersing the protein-based fibers in a container of water and an acid; dissolving the dye composition in a separate container of water, producing a dye solution; adding to the dye solution sodium sulfate and an acidic compound, such as acetic acid, sulfuric acid, propionic acid, phosphoric acid, and mixtures thereof; and stirring the protein-based fibers into the dye solution and heating the solution to produce colored protein-based fibers. The fibers may be, but are not limited to, textile fibers, such as wool and silk, and carpet fibers.
The present invention additionally provides a process of dyeing cellulose-based materials and the resultant colored cellulose-based materials. The process includes providing a dye composition prepared according to the process steps as set forth above; immersing the cellulose-based fibers in a container of water; dissolving the dye composition in a container of water, producing a dye solution; adding to the dye solution sodium sulfate and an acidic compound, such as acetic acid, sulfuric acid, propionic acid, phosphoric acid, or a mixture of these acids; and soaking the cellulose-based materials in the dye solution and heating the solution to produce colored cellulose-based materials.
The present invention also provides a dye composition comprising sulfonated oxidation products that produces a variety of hues for dyeing protein-based fibers and cellulose-based materials. In addition, the dye composition is resistant to fading from both light and washing, and has a low-cost of manufacture.